Background: In young females, obesity acts as a loading stimulus thus incrementing both skeletal muscle strength (1) and size (2). Nonetheless, the rate of change on skeletal muscle strength and size are in fact exacerbated in obese/highly adipose females (2). Studies show a gender difference in skeletal muscle volume responsiveness to BMI-induced loading (3). Therefore, we hypothesised that obesity would exacerbate the deleterious impact of ageing on skeletal muscle specific force in a male population. Method: Thirty-four untrained healthy males categorised by age into young (Y) (mean ± SD: 25.3 ± 9.6 yrs) versus old (O) (68.7 ± 7.2 yrs) were recruited to take part in this study. Body fat was assessed using dual-emission X-ray absorptiometry. Plantar flexion maximum voluntary isometric contraction (MVC) torque was assessed in the dominant limb using an isokinetic dynamometer at 0 deg (neutral ankle position) plantar flexion. MVC joint torque was corrected for voluntary muscle activation level (assessed using the interpolated twitch technique) and antagonist muscle co-activation (assessed via surface EMG) and classified as net MVC (nMVC). Gastrocnemius medialis (GM) muscle volume (V) was measured using B-mode ultrasonography and this allowed GM intrinsic strength (nMVC/V) and specific force (SF) to be calculated.Results: BMI was positively associated with nMVC (Y r=0.688; p=0.005; O r=0.538; p=0.021) and V (Y r=0.762; p=0.002; O r=0.471; p=0.049). BMI correlation against GM SF was positive in the younger cohort (Y r=0.773; p=0.018) but not the old (O r=0.14; p>0.05), so that the difference between the two slopes was statistically significant (Y vs. O being 0.879 N/cm2/BMI vs. 0.145 N/cm2/BMI; student t-statistic 2.05, p<0.05). Total body adiposity elicited similar positive associations with nMVC (Y r=0.520; p=0.047; O r=0.585; p=0.011) and V (Y r=0.708; p=0.005; O r=0.548; p=0.019). Interestingly the rate of ageing, implied through regression slopes, in terms of both intrinsic strength (-0.639 Ncm/cm3/year p=0.013) and GM SF (-0.373 N/cm2/year; p=0.013) was significantly steeper in the obese (i.e. high BMI). Similarly, the rate of ageing in terms of both GM V (-1.577cm3/year; p<0.05) and GM SF (-0.183 N/cm2/year; p<0.05) was found to be faster in the highly adipose.Conclusion: This study demonstrates that whilst high BMI (in spite of high adiposity) has a positive loading effect on absolute torque and muscle volume in young males, in older males, presence of obesity is detrimental to skeletal muscle function. Specifically the implied rate of ageing, at the fascicular level, suggests that the endocrine effects of combined adiposity and ageing may be additive. This effect would override the mechanical loading of chronic high loads and hence impede the physiological pathways responsible for muscle function optimization.